The primary goal of this research is to identify significant modifiable factors (i.e., diet, lifestyle factors, etc.) and novel risk factors that may predict the risk for GDM and contribute to the prevention of GDM. Within the common theme of insulin resistance and secretion, several important diet and lifestyle associations with GDM have been successfully identified in this effort based on data from the Nurses' Health Study II and the NICHD Fetal Growth Studies. In the past year, we observed that women taking supplemental vitamin D before pregnancy had a lower GDM risk. We also recently completed an invited review on iron supplementation and GDM and found accumulating evidence suggesting a potential link between greater iron stores or status during pregnancy and an elevated risk of GDM . In addition, in a large prospective cohort study, pre-pregnancy habitual folate intake, particularly supplemental folate intake, was inversely associated with risk of GDM. GDM has substantial burden on the health of mothers and children, and folic acid supplementation among women of reproductive age has been a widely adopted as a, low-cost intervention to reduce neural tube defects and with replication could offer an novel avenue to reduce the risk of GDM. Lastly, we identified a significant link between type 2 diabetes genetic susceptibility as characterized by 112 risk SNPs and GDM risk. Eight novel GDM SNPs were identified. These findings offer the potential to improve our understanding of the etiology of GDM, and particularly of biological mechanisms related to beta cell function. Several papers are submitted and under review.